Large-size special-shaped silicon nitride-based ceramic pillar and preparation method and application thereof

Abstract

The invention belongs to the technical field of ceramic materials, and particularly relates to a large-size special-shaped silicon nitride-based ceramic support column and a preparation method and application thereof. The large-size special-shaped silicon nitride-based ceramic pillar is prepared from the following basic raw materials in percentage by mass: 70-85% of industrial alumina powder, 2-3.5% of a sintering aid, 2-5% of washed clay, 5-20% of micron silicon nitride powder, 3-5% of a nano filler, an additional dopant accounting for 0.1-0.6% of the mass of the basic raw materials, a water reducing agent accounting for 0.2-0.3% of the mass of the basic raw materials and 31-35% of the mass of the basic raw materials, the washed clay is clay which is dried after washing treatment. The silicon nitride-based ceramic pillar prepared by the invention is high in surface flashover voltage, low in dielectric loss and dielectric constant and high in electric breakdown resistance, and can be used as an internal insulation pillar of power equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic materials, and particularly relates to a large-sized special-shaped silicon nitride-based ceramic pillar, a preparation method thereof, and an application thereof. Background Art

[0002] Since the 1960s, epoxy composites have been widely used in the power industry and continue to this day due to their relatively low economic cost and strong design adaptability. However, with the rapid growth of social electricity demand, the continuous increase in voltage levels, and the trend towards miniaturization of equipment structures, due to factors such as material aging and poor thermal stability of epoxy resin materials, their surface insulation performance may be difficult to meet the requirements for long-term stable operation in complex environments such as wall bushings and GIS. As a result, the safety and reliability issues of pillar insulators have become increasingly prominent.

[0003] Ceramic materials have good insulation, mechanical, anti-aging, corrosion-resistant and other characteristics, and are commonly used as insulating support structure materials for traditional power equipment. However, traditional ceramic materials are difficult to be compatible with the SF6 gas environment under complex working conditions such as high gas pressure, high electric field strength, and large temperature gradient for a long time, and cannot be directly used for the design and manufacture of internal pillar insulators of equipment such as wall bushings. Therefore, in existing research and reports, ceramic pillars are mainly used as outdoor insulators.

[0004] Therefore, how to design a ceramic pillar with high surface insulation strength and strong compatibility with SF6 gas so that it can be used as an internal insulator has become the focus of current research. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a large-sized special-shaped silicon nitride-based ceramic pillar with a high surface flashover voltage, low dielectric loss and dielectric constant, and strong electric breakdown resistance, which can be used as an internal insulating pillar of power equipment. Its preparation method adopts an atmospheric-pressure non-atmosphere sintering method, which is safe, environmentally friendly, energy-saving and consumption-reducing.

[0006] The large-sized special-shaped silicon nitride-based ceramic pillar described in the present invention has raw materials for preparation including the following basic raw materials in mass percentages: 70-85% of industrial alumina powder, 2-3.5% of sintering aids, 2-5% of washed clay, 5-20% of micron-sized silicon nitride powder, 3-5% of nano fillers, as well as 0.1-0.6% of additional dopants, 0.2-0.3% of water reducing agents, and 31-35% of water based on the mass of the above basic raw materials; among them, industrial alumina powder, nano fillers, sintering aids, washed clay, additional dopants, water reducing agents, and water are used as component A raw materials, and micron-sized silicon nitride powder and nano fillers are used as component B raw materials; the washed clay is clay dried after being washed.

[0007] The industrial alumina powder is spherical alumina powder, with the α-Al2O3 content not less than 98% and the median particle size of 3.3 - 4.8 μm.

[0008] The present invention uses industrial alumina powder as the main ceramic raw material. On the one hand, it is because the industrial alumina powder has few impurities, high purity, high corundum phase content and low price, which can reduce the product cost; on the other hand, because alumina ceramics have excellent mechanical properties, appropriate dielectric constant, high insulation and chemical stability, etc., it has obvious advantages when applied to electronic components.

[0009] The sintering aid is at least one of talc powder, wollastonite, barium carbonate, yttrium oxide. In addition to promoting sintering, the sintering aid can also change the size and shape of the ceramic lattice, and improve the gloss and electrical properties of the product.

[0010] The clay is at least one of Zuoyun clay, Inner Mongolia clay, Jilin ball clay. During the water washing treatment, the clay is added to water and soaked for more than 24 hours, then stirred for more than 5 minutes, and after standing, the upper floating foam and other impurities are poured out. The above steps are repeated by adding water again until the water is clear and there is no obvious floating matter. The washed clay is dried at a temperature of 80 - 100 °C and pulverized for standby. The water washing treatment can remove impurities such as organic components in the clay, which is beneficial to improving the various properties of the ceramic material.

[0011] The micron silicon nitride powder has a purity greater than 99%, its α conversion rate is not less than 95%, and the median particle size is 3.0 ± 0.5 μm.

[0012] Silicon nitride ceramics have high flexural strength, fracture toughness and wear resistance. In the present invention, a certain amount of silicon nitride powder is incorporated into the industrial alumina powder. In addition to utilizing the excellent properties of silicon nitride itself, when it is fired together with alumina powder, partial sialon solid solution can be formed, thereby reducing the firing temperature, realizing the atmospheric pressure sintering of the product, and reducing the energy (source) consumption and production cost.

[0013] The nano filler is at least one of nano silicon dioxide, nano alumina, nano silicon nitride powder. The purity of the nano filler is greater than 99%, and the particle size is between 10 - 30 nm.

[0014] During the use of the insulating pillars inside power equipment, problems such as surface flashover and electrical breakdown may occur. In the present invention, by introducing nano-fillers, the microstructure of the ceramic insulating material can be significantly improved, the generation of voids can be reduced, and the porosity can be lowered. At the same time, the high activity and large specific surface area of the nano-fillers can be utilized to control the crystal size and structure and reduce lattice defects. The reduction of porosity, the control of crystal size, and the reduction of lattice defects can all improve the surface quality of the ceramic material, reduce the generation of pits, and lower the surface roughness, thereby increasing the surface flashover voltage of the insulating material. Meanwhile, the refinement and uniformity of the grains and the reduction of lattice defects can, to a certain extent, reduce the dielectric loss and dielectric constant of the material. The reduction of the dielectric constant can improve the insulation performance of the material, thus better shielding the external electric field, reducing the polarization of electrons and ions, and decreasing the electric field strength inside the material, thereby enhancing its electrical breakdown resistance.

[0015] The external dopant is at least one of barium titanate, calcium copper titanate, and lanthanum-doped titanate.

[0016] In the present invention, a small amount of titanate is added as an external dopant. By utilizing the inhibitory effect of titanate on the conductive channels in the alumina ceramic lattice, the change in crystal phase orientation, and the influence on the ionic radius, the dielectric loss of the ceramic material can be reduced and the breakdown voltage of the ceramic material can be increased.

[0017] The water reducing agent is at least one of diethanolamine for ceramics and non-ionic polyacrylamide. The amino water reducing agent replacing the traditional water reducing agent can reduce the introduction of additional polar ions (such as Na + ).

[0018] The water is preferably deionized water.

[0019] The preparation method of the large-sized special-shaped silicon nitride-based ceramic pillar of the present invention includes the following steps:

[0020] (1) First, mix and ball-mill the raw materials of component A to obtain a ceramic slurry. After the ceramic slurry is dried, add the raw materials of component B and perform dry mixing and grinding to obtain a mixed powder.

[0021] (2) Age the mixed powder, and then perform forming and trimming to obtain a ceramic green body.

[0022] (3) Dry, pre-fire, and finally fire the ceramic green body in sequence to obtain the large-sized special-shaped silicon nitride-based ceramic pillar.

[0023] In step (1), in the ceramic slurry obtained after mixing and ball-milling, the particle size D50 ≤ 5 μm, and the content of particles with a particle size < 10 μm is higher than 85%.

[0024] In step (1), the ceramic slurry is dried until the moisture content is ≤ 1.5 wt.%, and then component B raw materials are added for mixing and dry grinding.

[0025] In step (1), it is preferred to use an alumina ball mill for ball milling and dry grinding. The ball milling time is 6 - 8 h, and the dry grinding time is 10 - 12 h. The present invention adopts a method of classified ball milling and mixing, first wet milling and then dry milling. On the one hand, it avoids using absolute ethanol, and at the same time can effectively avoid the disadvantage that the generation of gas when silicon nitride powder meets water will cause danger. On the other hand, dry grinding can improve the dispersion of nano fillers and prevent the structural inhomogeneity caused by powder agglomeration.

[0026] In step (2), during the aging process, according to the mass - volume ratio of the mixed powder and water of 1 kg:(3 - 5) ml, water is sprayed into the mixed powder, and they are mixed evenly under sealed conditions and left to stand and age for 48 - 96 h. In the present invention, a small amount of water is sprayed into the mixed powder, which can improve the difficulty of trimming the mixed powder due to too low moisture content. Standing and aging can make the sprayed water penetrate more evenly into the mixed powder, improve the fluidity of the powder, and is beneficial to the stability of molding.

[0027] In step (2), during molding, the aged mixed powder is filled into a mold, first subjected to an initial pressure of 30 - 40 MPa, demolded after the initial pressure, placed in a vacuum bag, and then cold isostatic pressing molding is carried out after vacuuming.

[0028] In step (3), the drying time is 72 - 120 h, and the drying temperature is 45 ± 5 °C; the pre - sintering adopts a belt - firing method, the highest pre - sintering temperature is 1220 - 1270 °C, and the pre - sintering time is 120 - 148 h; the highest final - sintering temperature is 1560 - 1625 °C, and the final - sintering time is 36 - 72 h. The present invention adopts a two - stage sintering process of pre - sintering first and then final - sintering. During pre - sintering, the dried ceramic blank is fired with other insulator products in the kiln by belt - firing, without the need for separate firing, which can effectively reduce the final - sintering time. Moreover, the products of the present invention have a long sintering time and a slow temperature rise, which is more conducive to the removal of organic and other impurity components and improves the density of the pre - sintered parts.

[0029] The application of the large - size special - shaped silicon nitride - based ceramic pillar described in the present invention is used as an internal insulating pillar of power equipment.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) In the raw material system of the present invention, a small amount of titanate external dopant and nano filler are introduced. By utilizing the inhibitory effect of titanate on the conductive channels in the alumina ceramic lattice, the change of crystal phase orientation, and the influence on the ionic radius, the dielectric loss of the ceramic material can be reduced, and the breakdown voltage of the ceramic material can be increased. At the same time, the nano filler can significantly improve the microstructure of the ceramic insulating material, reduce the generation of voids, lower the porosity, control the size and structure of the crystals, and reduce lattice defects, thereby increasing the surface flashover voltage of the insulating material, reducing the dielectric loss and dielectric constant of the material, and enhancing its electrical breakdown resistance ability.

[0032] (2) The raw materials of the present invention are divided into component A and component B. By adopting the method of hierarchical ball milling and mixing, first, the industrial alumina powder, nano filler, sintering aid, washed clay, external dopant, water reducing agent, and water in component A raw materials are mixed and wet milled. Then, the obtained ceramic powder is mixed and dry milled with the micron silicon nitride powder and nano filler in component B raw materials. On the one hand, the use of anhydrous ethanol is avoided, and at the same time, the disadvantage that the silicon nitride powder generates gas when encountering water, which may cause danger, can be effectively avoided, and the operation is simpler and safer. On the other hand, dry milling can improve the dispersibility of the nano filler and prevent the structural non-uniformity caused by powder agglomeration.

[0033] (3) The present invention adopts the method of secondary firing. The first firing adopts the method of belt firing without separate firing, which can effectively reduce the final firing time, improve the performance of the product, save energy and reduce consumption, and lower the production cost.

[0034] (4) The silicon nitride-based ceramic pillar prepared by the present invention has a high surface flashover voltage, low dielectric loss and dielectric constant, and strong electrical breakdown resistance ability, and can replace epoxy resin materials and be used as an internal insulating pillar for power equipment. Specific embodiments

[0035] The present invention will be further described below in conjunction with embodiments. The raw materials used in the embodiments are all commercially available conventional raw materials unless otherwise specified; the process methods used in the embodiments are all conventional methods in the art unless otherwise specified.

[0036] Some of the raw materials used in the embodiments are described as follows:

[0037] Industrial alumina powder: Spherical alumina powder, with the content of α-Al2O3 not less than 98%, and the median particle size of 3.3 - 4.8 μm;

[0038] Micron silicon nitride powder: The purity is greater than 99%, the α conversion rate is not less than 95%, and the median particle size is 3.0 ± 0.5 μm;

[0039] Nano silicon dioxide, nano alumina, nano silicon nitride powder: The purity is greater than 99%, and the particle size is between 10 - 30 nm.

[0040] In the examples, the treatment method of the washed clay is as follows:

[0041] Add the clay into water (there is no special requirement for the amount of water, and it is advisable that the water surface is more than 10 cm above the clay), soak for 24 h, then stir for 5 min. After standing, pour out the floating foam and other impurities on the upper layer, add water again and repeat the above steps until the water is clear and there are no obvious floating substances. Dry the washed clay at 100 °C and crush it for standby.

[0042] Example 1

[0043] Prepare large-sized special-shaped silicon nitride-based ceramic struts according to the following steps:

[0044] (1) Weigh the basic raw materials according to the following mass percentages: 70% of industrial alumina powder, 20% of micron silicon nitride powder, 5% of washed Zuoyun clay, 2% of talc powder, 3% of nano silicon nitride powder; in addition, weigh 0.2% of barium titanate, 0.3% of diethanolamine, and 31% of deionized water based on the mass of the above basic raw materials respectively;

[0045] Add the industrial alumina powder, talc powder, washed Zuoyun clay, barium titanate, diethanolamine, and deionized water, which are used as raw materials of component A, into an alumina ball mill, and mix and ball mill for 8 h to obtain a ceramic slurry with a particle size D50 ≤ 5 μm and a content of particles with a size < 10 μm higher than 85%;

[0046] Dry the above ceramic slurry until the water content ≤ 1.5 wt.%, and add it together with the micron silicon nitride powder and nano silicon nitride powder, which are used as raw materials of component B, into an alumina ball mill, and mix and dry mill for 12 h to obtain a mixed powder;

[0047] (2) According to the mass-volume ratio of the mixed powder to deionized water of 1 kg:3 ml, spray deionized water into the mixed powder, mix evenly under sealed conditions, and stand for aging for 72 h;

[0048] Fill the aged mixed powder into a mold, first perform initial pressing with a manual pressure pump at a pressure of 30 MPa, demold after initial pressing, place it in a vacuum bag, perform cold isostatic pressing after vacuuming, and then trim the blank to obtain a ceramic blank;

[0049] (3) After drying the ceramic blank at 45 ± 5 °C for 72 h, load it into a kiln for pre-firing together with other insulator products. The maximum pre-firing temperature is 1240 °C, and the firing time is 120 h. Then put it into a high-temperature furnace for final firing. The maximum final-firing temperature is 1590 °C, and the firing time is 48 h. Process the sample after final firing into a test block that can be tested for detection. After passing the post-kiln inspection, process the strut and wait for subsequent treatment.

[0050] Example 2

[0051] Prepare large-sized special-shaped silicon nitride-based ceramic struts according to the following steps:

[0052] (1) Weigh the basic raw materials according to the following mass percentages: 80% industrial alumina powder, 10% micron-sized silicon nitride powder, 2% washed Inner Mongolia clay, 3.5% wollastonite, 4.5% nano-sized silicon dioxide; in addition, weigh 0.6% of calcium copper titanate, 0.3% of diethanolamine, and 33% of deionized water respectively based on the mass of the above basic raw materials;

[0053] Add the industrial alumina powder, washed Inner Mongolia clay, wollastonite, calcium copper titanate, diethanolamine, and deionized water as raw materials of component A into an alumina ball mill, mix and ball mill for 6 h to obtain a ceramic slurry with a particle size D50 ≤ 5 μm and a content of particles with a size < 10 μm higher than 85%;

[0054] Dry the above ceramic slurry until the moisture content ≤ 1.5 wt.%, and then add it together with the micron-sized silicon nitride powder and nano-sized silicon dioxide as raw materials of component B into an alumina ball mill, mix and dry mill for 10 h to obtain a mixed powder;

[0055] (2) Spray deionized water into the mixed powder according to the mass-volume ratio of the mixed powder to deionized water of 1 kg:4 ml, mix evenly under sealed conditions, and let it stand and age for 96 h;

[0056] Fill the aged mixed powder into a mold, first carry out initial pressing through a manual pressure pump at a pressure of 35 MPa, demold after initial pressing, place it in a vacuum bag, carry out cold isostatic pressing after vacuuming, and then trim the blank to obtain a ceramic blank;

[0057] (3) After drying the ceramic blank at 45 ± 5 °C for 96 h, load it into a kiln together with other insulator products for pre-firing. The maximum pre-firing temperature is 1250 °C, the firing time is 136 h, then put it into a high-temperature furnace for final firing. The maximum final firing temperature is 1605 °C, the firing time is 36 h. The specimens after final firing are processed into test blocks that can be tested and detected. After passing the post-kiln inspection, process the struts and wait for subsequent treatment.

[0058] Example 3

[0059] Prepare large-sized special-shaped silicon nitride-based ceramic struts according to the following steps:

[0060] (1) Weigh the basic raw materials according to the following mass percentages: 85% industrial alumina powder, 5% micron-sized silicon nitride powder, 3% washed Jilin ball clay, 1% barium carbonate, 1% yttrium oxide, 3% nano-sized alumina powder, 2% nano-sized silicon dioxide powder; in addition, weigh 0.1% of lanthanum bismuth titanate, 0.2% of non-ionic polyacrylamide, and 35% of deionized water respectively based on the mass of the above basic raw materials;

[0061] Add industrial alumina powder, barium carbonate, yttrium oxide, washed Jilin ball clay, bismuth lanthanum titanate, non-ionic polyacrylamide, and deionized water, which are used as raw materials for Component A, into an alumina ball mill, and mix and ball mill for 7 h to obtain a ceramic slurry with a particle size D50 ≤ 5 μm and a particle size < 10 μm content higher than 85%;

[0062] Dry the above ceramic slurry until the moisture content ≤ 1.5 wt.%, and then add it together with micron silicon nitride powder, nano-alumina powder, and nano-silica powder, which are used as raw materials for Component B, into an alumina ball mill, and mix and dry mill for 11 h to obtain a mixed powder;

[0063] (2) Spray deionized water into the mixed powder according to the mass-volume ratio of the mixed powder to deionized water of 1 kg:5 ml, mix evenly under sealed conditions, and let it stand and age for 48 h;

[0064] Fill the aged mixed powder into a mold, first perform initial pressing with a manual pressure pump at a pressure of 40 MPa, demold after initial pressing, place it in a vacuum bag, perform cold isostatic pressing after vacuuming, and then trim the blank to obtain a ceramic blank;

[0065] (3) After drying the ceramic blank at 45 ± 5 °C for 120 h, load it into a kiln with other insulator products for pre-firing. The maximum pre-firing temperature is 1270 °C, and the firing time is 120 h. Then put it into a high-temperature furnace for final firing. The maximum final firing temperature is 1590 °C, and the firing time is 48 h. The samples after final firing are processed into test blocks for testing. After passing the post-kiln inspection, process the struts and wait for subsequent treatment.

[0066] Comparative Example 1

[0067] Epoxy strut materials and epoxy strut products for electrical insulation provided by a certain Italian company.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 is only that no dopant is added, that is, industrial alumina powder of equal mass is used to replace barium titanate.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 is only that no nano filler is added, that is, industrial alumina powder of equal mass is used to replace nano silicon nitride.

[0072] Comparative Example 4

[0073] The difference between this comparative example and Example 1 lies only in the firing process in step (3). The preparation process of this comparative example is as follows: After drying the ceramic green body at 45 ± 5 °C for 72 h, it is directly put into a high-temperature furnace for final firing. The highest final firing temperature is 1620 °C, and the firing time is 72 h.

[0074] The silicon nitride-based ceramic materials prepared in Examples 1 - 3 and Comparative Examples 2 - 4, as well as the epoxy support material of Comparative Example 1, are processed into standard test strips for performance testing. Among them, the flexural strength is tested with reference to the standard GB / T 6569 - 2006, the volume resistivity is tested with reference to the standard IEC 62631 - 3 - 1:2016, the dielectric constant and dielectric loss are tested with reference to the standard GB / T 5594.4 - 2015, the flashover voltage is tested with reference to the standard IEC 60243 - 1 - 2013, and the breakdown field strength is tested with reference to the standard GB / T 1408. The test results are shown in Table 1.

[0075] Table 1 Performance test results of silicon nitride-based ceramic material standard test strips

[0076]

[0077] As can be seen from Table 1, compared with Example 1, the epoxy material of Comparative Example 1 is an organic composite material. Although alumina powder is added, the improvement of mechanical properties is not significant, which mainly depends on the performance characteristics of the epoxy organic material itself; the dielectric constant and dielectric loss of Comparative Example 2 increase to some extent, and the flashover voltage decreases. It is analyzed that the lack of titanate makes the material lack the influence of the piezoelectric effect during the firing process, resulting in the change of grain orientation or excessive growth of ionic radius; the volume resistivity and flashover voltage of Comparative Example 3 decrease significantly. It is analyzed that this is due to the influence of the material microstructure. Without the presence of nano fillers, the porosity of the material itself increases, and the role of refining grains is also lost, and lattice defects will increase accordingly; Comparative Example 4 does not use pre-firing but directly fires, which requires increasing the firing time and raising the final firing temperature. Even so, there will be a significant difference in the densification of the ceramic microstructure. This is mainly because during the firing process of the ceramic material, a series of processes such as removing moisture, organic carbon chains, and completing the phase transformation need to be carried out at appropriate temperatures and times.

[0078] In addition, in order to compare the performance of the insulator support during application, the silicon nitride-based ceramic supports prepared in Example 1 and Comparative Example 3, as well as the epoxy support of Comparative Example 1, are assembled into products for performance testing. The results are shown in Table 2.

[0079] Table 2 Performance test results of silicon nitride-based ceramic supports

[0080] Project Flexural strength (under the condition of 16 kN) <![CDATA[Body density (g / cm 3 )]]> Porosity (%) Surface flashover under ±10 kV Example 1 No damage, no abnormal sound 3.872 0.213 No flashover, no obvious burn marks Comparative Example 1 No damage, no abnormal sound 1.985 0.405 No flashover, obvious fine burn marks Comparative Example 3 No damage, no abnormal sound 3.784 0.290 No flashover, no obvious burn marks

[0081] As can be seen from Table 2, compared with Example 1, the detection data of Comparative Example 1 are mainly related to the properties of the organic material itself, and the organic material itself is not resistant to ablation; the bulk density of Comparative Example 3 slightly decreases and the porosity increases. Compared with Example 1, although there is no obvious change in surface flashover, the flashover times or service life in actual application may be affected. This is mainly because during use, the charge accumulation, distribution uniformity and bearing capacity on the surface of the post insulator will deteriorate.

Claims

1. A large-sized special-shaped silicon nitride-based ceramic pillar, characterized in that: The raw materials for preparation include the following basic raw materials by mass percentage: 70-85% of industrial alumina powder, 2-3.5% of sintering aid, 2-5% of washed clay, 5-20% of micron-sized silicon nitride powder, 3-5% of nano filler, as well as 0.1-0.6% of additional dopant, 0.2-0.3% of water reducing agent, and 31-35% of water based on the mass of the above basic raw materials; among them, industrial alumina powder, nano filler, sintering aid, washed clay, additional dopant, water reducing agent, and water are used as component A raw materials, and micron-sized silicon nitride powder and nano filler are used as component B raw materials; the washed clay is clay dried after being washed.

2. The large-sized special-shaped silicon nitride-based ceramic pillar according to claim 1, wherein: The industrial alumina powder is spherical alumina powder, with its α-Al2O3 content not less than 98% and median particle size of 3.3-4.8 μm; The micron-sized silicon nitride powder has a purity greater than 99%, its α conversion rate is not less than 95%, and median particle size is 3.0±0.5 μm.

3. The large-sized special-shaped silicon nitride-based ceramic pillar according to claim 1, wherein: The sintering aid is at least one of talc powder, wollastonite, barium carbonate, and yttrium oxide; The clay is at least one of Zuoyun clay, Inner Mongolia clay, and Jilin ball clay.

4. The large-sized special-shaped silicon nitride-based ceramic pillar according to claim 1, wherein: The nano filler is at least one of nano silicon dioxide, nano alumina, and nano silicon nitride powder, with the purity of the nano filler greater than 99% and particle size between 10-30 nm.

5. The large-sized special-shaped silicon nitride-based ceramic pillar according to claim 1, wherein: The dopant is at least one of barium titanate, calcium copper titanate, and lanthanum-doped titanate; The water reducing agent is at least one of diethanolamine and non-ionic polyacrylamide.

6. A method for preparing a large-sized special-shaped silicon nitride-based ceramic pillar according to any one of claims 1-5, characterized in that: It includes the following steps: (1) First, mix and ball-mill the component A raw materials to obtain a ceramic slurry. After the ceramic slurry is dried, then add the component B raw materials and mix and dry-mill them to obtain a mixed powder; (2) Age the mixed powder, and then form and trim it to obtain a ceramic green body; (3) Dry, pre-fire, and finally fire the ceramic green body in sequence to obtain a large-sized special-shaped silicon nitride-based ceramic pillar.

7. The preparation method of the large-size special-shaped silicon nitride-based ceramic pillar according to claim 6, characterized in that: In step (1), in the ceramic slurry obtained after mixing and ball-milling, the particle size D50≤5 μm, and the content of particles with particle size <10 μm is higher than 85%.

8. The preparation method of the large-sized special-shaped silicon nitride-based ceramic pillar according to claim 6, characterized in that: In step (2), during aging, according to the mass-volume ratio of the mixed powder and water of 1 kg:(3-5) ml, spray water into the mixed powder, mix evenly under sealed conditions, and let it stand and age for 48-96 h.

9. The preparation method of the large-size special-shaped silicon nitride-based ceramic pillar according to claim 6, characterized in that: In step (3), the drying time is 72-120 h, and the drying temperature is 45±5 °C; the pre-firing is carried out in a belt-firing manner, the maximum pre-firing temperature is 1220-1270 °C, and the pre-firing time is 120-148 h; the maximum final-firing temperature is 1560-1625 °C, and the final-firing time is 36-72 h.

10. Application of the large-sized special-shaped silicon nitride-based ceramic pillar according to any one of claims 1-5, characterized in that: It is used as an internal insulating pillar in electrical equipment.

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